Acute renal failure (ARF), is a common lethal complication in critically ill patients and at least 50% of patients who develop this condition do not recover. It is of therefore particular importance to devise a means of monitoring renal function in real time so that the efficacy of the commonly employed therapeutic strategies for critically ill patients can be improved. While there exist several methods for estimating the physiological state of the kidneys during treatment in the ICU, these methods have such limitations in speed of response that they have not been satisfactory for directing the therapeutic interventions used to forestall acute renal failure in critically ill patients. The goal of the proposed program is to conduct the research necessary to improve the instrumentation and protocols for prompt measurement of glomerular filtration rate (GFR) from the clearance of radiolabeled DTPA for specific application in the treatment of critically ill patients in the ICU. An important benefit of this approach is that it will be possible to administer relatively small doses of relevant pharmaceuticals such as dopamine and phenylephrine to both stable and critically ill patients and to obtain extremely useful data regarding the behavior of these drugs in general and the response of patients at high risk in particular.